JP2008000324A - Gradient magnetic field coil apparatus for nuclear magnetic resonance imaging system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a void can be caused in a gradient magnetic field coil apparatus for an MRI produced by resin impregnation. <P>SOLUTION: Between a Z-axis gradient magnetic field coil 11 and an X-axis gradient magnetic field coil 12, and between the X-axis gradient magnetic field coil 12 and a Y-axis gradient magnetic field coil 13, two or more tape-state insulators 51 are arranged with intervals therebetween in parallel with the surface of the coils. Resin injected by a die not shown in the figure flows with intervals between the tape-state insulators 51 as channels 71 for impregnation and the resin is hardened. Thus, the gradient magnetic field coil apparatus which has no void and which has satisfactory insulation is produced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a nuclear magnetic resonance imaging apparatus (MRI apparatus), and more particularly to a gradient magnetic field coil thereof.

  In diagnosis using an MRI apparatus, a gradient magnetic field is superimposed on a static magnetic field in order to limit the excitation range and acquire spatial position information of a magnetic resonance signal. The gradient magnetic field is a Z-axis gradient magnetic field whose gradient spatial direction is parallel to the static magnetic field, an X-axis gradient magnetic field whose magnetic field gradient is orthogonal to the static magnetic field, and a Y-axis whose magnetic gradient gradient is orthogonal to the static magnetic field and the X axis. There are three types of gradient magnetic fields. In general, a set of three types of gradient magnetic field coils corresponding to these three axes is molded by a solid insulator, and incorporated in an MRI apparatus as a gradient magnetic field coil apparatus.

  In recent years, high-speed diagnosis and high-definition diagnostic images have been demanded, and the performance of nuclear magnetic resonance imaging apparatuses has been improved. Improvement of gradient magnetic field performance is also an issue. The gradient magnetic field is generated in a pulse shape based on an arbitrary sequence. In order to realize high-speed diagnosis, it is required to shorten the time required to reach a desired magnetic field (called rise time). This means that the rise time of the energization current of the gradient magnetic field coil is shortened, but when the rise time is shortened, a high voltage is generated in the coil due to the inductance and resistance of the gradient magnetic field coil. In particular, since a high voltage is generated between the X, Y, and Z axis gradient magnetic field coils, it is necessary to enhance the insulation performance.

  When voids (voids) exist in the insulator due to incomplete insulation treatment, partial discharge occurs in the voids. Partial discharge occurs when the product of void size and pressure reaches a discharge voltage defined by Paschen's law. Since it is not a discharge due to a short circuit, the amount of discharge per discharge is small, but the insulator is gradually deteriorated, and the coil is eventually short-circuited. In order to prevent partial discharge, it is desirable to eliminate voids that are the cause. In Patent Document 1, a groove is formed on the surface of the coil winding to improve the flow of the resin, to prevent voids in the resin impregnated between the windings of the coil winding, and to insulate the coil winding. A method for improving the above is disclosed.

JP 2004-73288 A

  In the method of Patent Document 1, since a groove is formed on the coil surface, the winding in the grooved portion has a small cross-sectional area, and partial overheating due to Joule heat generation becomes a problem. Moreover, the cost for processing a groove | channel also generate | occur | produces.

  An object of the present invention is to provide a gradient magnetic field coil capable of reliably impregnating a resin without forming a groove on the coil surface and improving the insulation characteristics because no void is generated, and a nucleus using the same. The object is to provide a magnetic resonance imaging apparatus (MRI apparatus).

  In order to achieve the above object, the present invention is a gradient magnetic field coil device for applying a gradient magnetic field to a subject in a static magnetic field by a nuclear magnetic resonance imaging apparatus (MRI apparatus), wherein the gradient magnetic field coil is a spiral winding. It includes a plurality of coils formed by planarly forming a line pattern, a plurality of tape-like insulators arranged at intervals between the coils, and a resin impregnated in the intervals.

  In addition, the gradient magnetic field coil includes a plurality of coils that are formed by laminating a spiral winding pattern in a plane, and a plurality of tape-like insulators arranged between the coils. And a resin impregnated and cured. In this configuration, since the impregnating resin flows between the tape-like insulators, there is a feature that generation of voids in the resin can be prevented.

  Further, the gradient magnetic field coil includes a plurality of coils formed by planarly forming a spiral winding pattern, a plurality of tape-like insulators disposed in order between the coils, an insulating sheet, and a plurality of coils The tape-shaped insulator and the plurality of tape-shaped insulators are arranged at intervals, and the resin is impregnated into the intervals and cured. According to this configuration, even if a void is formed between the coils, there is a feature that an electrical short circuit can be prevented by the insulating sheet.

  According to the present invention, in the gradient magnetic field coil apparatus of the nuclear magnetic resonance imaging apparatus (MRI apparatus), the resin can be impregnated with certainty, so that no voids are generated and the insulating characteristics can be improved.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 4 shows the arrangement of coil groups in an MRI apparatus called a vertical magnetic field type. A pair of upper and lower static magnetic field generating coils 101 are arranged, and a shim coil 22, an X axis gradient magnetic field coil 12, a Y axis gradient magnetic field coil 13, a Z axis gradient magnetic field coil 11, and an RF coil 21 are arranged.

  The static magnetic field generating coil 101 generates a static magnetic field at a desired position of the subject 201. The source of the static magnetic field may be a permanent magnet in addition to the coil. The static magnetic field causes the subject 201 to generate nuclear magnetic resonance. The resonance frequency is proportional to the strength of the static magnetic field. Although the proportionality constant varies depending on the atom, for example, in the case of a hydrogen atom, the resonance frequency is 100 MHz at a magnetic field strength of 2.34T. A static magnetic field requires a uniform magnetic field in an arbitrary region of the subject 201, and an allowable error is about 1 / 1,000,000 in a sphere having a diameter of 30 cm.

  The gradient coil is composed of a Z-axis gradient coil 11, an X-axis gradient coil 12, and a Y-axis gradient coil 13. The Z-axis gradient magnetic field coil 11 generates a gradient magnetic field in a direction parallel to the static magnetic field generated by the static magnetic field generator 101. The X axis gradient magnetic field coil 12 generates a gradient magnetic field in a direction perpendicular to the static magnetic field generated by the static magnetic field generator 101, and the Y axis gradient magnetic field coil 13 is inclined in a direction perpendicular to the static magnetic field direction and the X axis gradient magnetic field direction. Generate a magnetic field. In FIG. 1, the Y-axis gradient magnetic field coil 13, the X-axis gradient magnetic field coil 12, and the Z-axis gradient magnetic field coil 11 are arranged in the order close to the subject, but the arrangement order is not limited to this.

  The RF coil 21 irradiates the subject with high frequency, receives an NMR signal (nuclear magnetic resonance signal) generated from the subject, and obtains a tomographic photograph of the subject by performing predetermined signal processing. The shim coil 22 is a coil for correcting non-uniformity of the static magnetic field generator 101.

  5 is an explanatory diagram showing the direction of the magnetic field of the Z-axis gradient magnetic field coil, FIG. 6 is an explanatory diagram showing the direction of the magnetic field of the X-axis gradient magnetic field coil, and FIG. 7 is an explanatory diagram showing the direction of the magnetic field of the Y-axis gradient magnetic field coil. It is. In these drawings, 30 indicates a current, 31 indicates a magnetic field, and 32 indicates a direction of a gradient magnetic field. The coil is drawn as a one-turn circular coil or a half-moon-shaped coil, but in reality it may be a multi-turn coil or a different shape.

  In the vertical magnetic field type MRI apparatus, the static magnetic field B0 is in the Z direction. When the coils in these figures are energized, a magnetic field is generated in the direction of Bx, By or Bz in the figures. These magnetic fields are combined to generate a Z-direction magnetic field whose intensity is inclined in the Gx, Gy, or Gz direction. By using these gradient magnetic fields, the excitation range is limited and the spatial position information of the magnetic resonance signal is acquired.

  There are other horizontal magnetic field types in the MRI system, and since the arrangement of the magnet generating the static magnetic field and the subject is different, the shape of the gradient magnetic field coil is also different, but basically in the X-axis, Y-axis, and Z-axis directions. The generation of the gradient magnetic field is the same as the vertical magnetic field type.

  The gradient magnetic field coil apparatus of the MRI apparatus according to the present invention includes a Z-axis coil, an X-axis coil, and a Y-axis coil in which a spiral winding pattern is formed and stacked, and a plurality of tape-like insulators between these coils. Are arranged at intervals. When the resin is injected into the gradient coil disposed in the mold, the resin flows through the space between the tape-shaped insulators and is impregnated and cured.

  A first embodiment of the present invention will be described. FIG. 1 is a partial sectional view of a gradient coil apparatus according to a first embodiment. Between the Z-axis gradient magnetic field coil 11, the X-axis gradient magnetic field coil 12, and the Y-axis gradient magnetic field coil 13, a plurality of tape-like insulators 51 are arranged by appropriate gaps to provide an inter-coil gap 71, and this gap is provided. Impregnated with resin.

  FIG. 2 shows an outline of a sectional view of the gradient coil showing its detailed structure. The Z-axis gradient magnetic field coil 11 and the X-axis gradient magnetic field coil 12 have a gap 71 between the coils secured by a plurality of tape-like insulators 51 arranged with an appropriate gap, and are impregnated with a resin 61. Further, the same structure is provided between the X-axis gradient magnetic field coil 12 and the Y-axis gradient magnetic field coil 13. Between the coils, the resin 61 flows through the resin flow path 71 and is impregnated.

  The gradient coil for each axis is made of a metal having a low electrical resistance such as copper. The X-axis gradient magnetic field coil 12, the Y-axis gradient magnetic field coil 13, and the Z-axis gradient magnetic field coil 11 have a shape in which a flat plate metal is cut into a spiral shape. Also good.

  The tape-like insulator 51 is preferably a polyethylene terephthalate resin (PET), a polyimide resin (PI) or the like. Furthermore, you may comprise the tape-shaped insulator 51 with glass fiber. Thereby, when the resin 61 penetrates into the glass fiber, the strength of the resin 61 can be increased, and the cracking of the resin 61 can be prevented. The tape-like insulator 51 has a width of 10 mm or more and a thickness of 10 μm or more. The longitudinal direction and the width direction of the tape-shaped insulator 51 are parallel to the coil surface, and the thickness direction is vertical. The resin 61 is preferably an epoxy resin or the like.

  FIG. 3 is an explanatory diagram of a method for assembling the gradient coil apparatus. First, a plurality of tape-like insulators 51 are arranged on the Y-axis gradient magnetic field coil 13. On this, the X-axis gradient magnetic field coil 12, the tape-like insulator 51, and the Z-axis gradient magnetic field coil 11 are arranged. At this time, the tape-like insulator 51 is arranged in parallel with an appropriate gap 71. These are put in a mold, and the resin 61 flows through the resin flow channel 71 to be impregnated and cured to form a gradient magnetic field coil device.

  The gradient magnetic field coil configured in this manner is arranged in a mold (not shown), and resin is injected from the outside. The resin 61 forms a coil frame on the outside of the coil and flows through the resin flow path 71 between the coils to be impregnated and cured.

  In FIG. 3, the tape-like insulator 51 is arranged in parallel, but the tape-like insulator 51 is arranged radially from the coil center as long as a passage through which the resin flows when impregnating the resin can be secured. The structure to do may be sufficient. In FIGS. 2 and 3, only the X, Y, and Z axis gradient magnetic field coils are drawn. However, a shield coil for shielding a magnetic field generated by these coils and a shim coil for correcting a static magnetic field are included. But you can.

  According to the first embodiment, the gap between the tape-like insulators 51 becomes the resin flow path 71, and the resin 61 smoothly flows and impregnates the resin flow path 71, so that the resin can be reliably impregnated and voids are generated. Therefore, the insulation characteristics can be remarkably improved.

  A second embodiment according to the present invention will be described. FIG. 8 schematically shows a cross-sectional view of the gradient coil apparatus according to the second embodiment. Between the Z-axis gradient magnetic field coil 11 and the X-axis gradient magnetic field coil 12, a plurality of tape-like insulators 51 arranged with an appropriate gap 71 are arranged in two layers, and an insulation sheet is provided between the tape-like insulators 71. 81 is arranged. Further, the same structure is provided between the X-axis gradient magnetic field coil 12 and the Y-axis gradient magnetic field coil 13.

  The gradient magnetic field coil configured in this manner is arranged in a mold (not shown), and resin is injected from the outside. The resin 61 is impregnated by flowing through the resin flow path 71 between the coils. Further, the resin blocked by the insulating sheet 81 flows into the lower resin flow path 71 from the gap between the mold and the mold.

  The gradient coil for each axis is made of a metal having a low electrical resistance such as copper. The tape-like insulator 51 is preferably polyethylene terephthalate resin (PET), polyimide resin (PI) or glass fiber. The tape-like insulator 51 has a width of 10 mm or more and a thickness of 10 μm or more. The longitudinal direction and the width direction of the tape-like insulator 51 are parallel to the coil surface, and the thickness direction is vertical. The insulating sheet 81 is preferably made of polyethylene polyethylene terephthalate resin (PET), polyimide resin (PI), or the like. The insulating sheet 81 is sized to substantially cover the gradient magnetic field coils of each axis, and is sandwiched between the tape-like insulators 51.

  FIG. 9 is an explanatory view showing a method of assembling the gradient coil apparatus according to the second embodiment. First, a plurality of tape-like insulators 51 are arranged on the Y-axis gradient magnetic field coil 13 with a gap. Next, the insulating sheet 81, the plurality of tape-like insulators 51, and the X-axis gradient magnetic field coil 12 are disposed in this order. Further, a plurality of tape-like insulators 51, an insulating sheet 81, a plurality of tape-like insulators 51, and a Z-axis gradient magnetic field coil 11 are arranged in this order. The tape-shaped insulator 51 is arranged in parallel with an appropriate gap. These are put in a mold and impregnated with resin 61 and cured to form a gradient coil device.

  In FIG. 9, a configuration in which the tape-like insulators 51 are arranged in parallel is adopted, but the tape-like insulators 51 are arranged radially from the coil center as long as a passage through which the resin flows when the resin is impregnated can be secured. It may be configured. 8 and 9, only the gradient magnetic field coils of the X, Y, and Z axes are drawn. However, a shield coil for shielding the magnetic field generated by these and a shim coil for correcting the static magnetic field are provided. May be included.

  According to the second embodiment, the gap between the tape-like insulators 51 becomes the resin flow path 71, and the resin flows smoothly through the resin flow path 71 during the resin impregnation, and voids are not easily generated. Further, since the insulating sheet 81 is disposed between the coils, even if a void occurs in the resin 61, the insulating sheet 81 can prevent a short circuit between the coils. As described above, since the resin can be reliably impregnated and the short circuit between the coils can be prevented, the insulation characteristics between the coils can be further improved.

The fragmentary sectional view of the gradient magnetic field coil apparatus by Example 1 of this invention. FIG. 3 is a cross-sectional view of the gradient coil according to the first embodiment. Explanatory drawing which shows the assembly method of the gradient magnetic field coil by Example 1. FIG. The block diagram of the magnetic field generator in an MRI imaging apparatus. Explanatory drawing of a Z-axis gradient magnetic field coil. Explanatory drawing of an X-axis gradient magnetic field coil. Explanatory drawing of a Y-axis gradient magnetic field coil. Sectional drawing of the gradient magnetic field coil by Example 2. FIG. Explanatory drawing which shows the assembly method of the gradient magnetic field coil by Example 2. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Gradient magnetic field coil apparatus, 11 ... Z-axis gradient magnetic field coil, 12 ... X-axis gradient magnetic field coil, 13 ... Y-axis gradient magnetic field coil, 21 ... RF coil, 22 ... Shim coil, 30 ... Current, 31 ... Magnetic field, 32 ... Gradient magnetic field direction 51 ... Tape-like insulator, 61 ... Resin, 71 ... Resin flow path, 81 ... Insulating sheet, 101 ... Static magnetic field generating coil, 201 ... Subject.

Claims (6)

A gradient coil device that applies a gradient magnetic field to a subject in a static magnetic field by a nuclear magnetic resonance imaging apparatus (MRI apparatus),
The gradient magnetic field coil is formed by laminating a plurality of coils formed in a spiral winding pattern in a plane, a plurality of tape-like insulators arranged with a space between the coils, and impregnating and hardening the space. And a gradient magnetic field coil device. A gradient coil device that applies a gradient magnetic field to a subject in a static magnetic field by a nuclear magnetic resonance imaging apparatus (MRI apparatus),
The gradient magnetic field coil has a spiral winding pattern formed in a planar manner and a plurality of laminated coils, and a plurality of tape-like insulators are arranged between the coils, and the gap is impregnated and cured. And a gradient magnetic field coil device. A gradient coil device that applies a gradient magnetic field to a subject in a static magnetic field by a nuclear magnetic resonance imaging apparatus (MRI apparatus),
The gradient magnetic field coil includes a plurality of coils that are formed by laminating a spiral winding pattern in a plane, a plurality of tape-like insulators arranged in order between the coils, an insulating sheet, and a plurality of tapes. And a plurality of tape-like insulators arranged at intervals and a resin impregnated and cured in the intervals.   4. The gradient magnetic field coil device according to claim 1, wherein the gradient magnetic field coil includes a Z-axis gradient magnetic field coil, an X-axis gradient magnetic field coil, and a Y-axis gradient magnetic field coil.   5. The gradient magnetic field coil device according to claim 1, wherein the tape-like insulator is made of glass fiber.   A magnetic resonance imaging apparatus comprising the gradient magnetic field coil according to claim 1.

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